Electron-discharge device



Aug. 26. 1924.

W. C. WHITE ELECTRON DISCHARGE DEVICE Filed 001:. 28 1920 Fig. 2.

20 25 FLA TE VOLTAGE l5 PLATE VOLTAGE Fig. 4.

Inventor: 1 William Owhit e,

GRID VOLT/16E His Attorneg.

Patented Aug. 26, 1924.

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WILLIAM C. WHITE, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YO'RK.

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Application fil ed October 28, 1920. Serial No. 420,231.

To all whom it may concern. 4

Be it known that I, WILLIAM C. WHITE, a citizen of the United States,residing at Schenectady, in the county of Schenectady, State of NewYork, have invented certain new and useful Improvements in Electron-Discharge Devices, of which the following is a specification.

My present invention relates to electrical amplifying and radiodetecting devices in which an electron current is controlled byrelatively feeble voltage variations.

Two classes of radio detectors of the electron valve type haveheretofore been employed.

(1) Detectors of the audion, or soft valve, type which contained enoughresidual gas to give the device a critical characteristic, that is, aregion of instability at which the device was sensitive to radioimpulses due to gas ionization.

This class of detectors were erratic in behavior. A given impressedvoltage did not always produce a given effect. Tubes apparentlyidentical in construction varied in operating characteristics and agiven tube would progressively change in operating characteristics.

(2) Detectors of the pliotron, or hard valve, type in which theevacuation was so complete that gas ionization was negligible and didnot afi ect the operation of the devlce.

This class of detectors although not so sensitive as the best of thefirst class are regular and reproducible "in operation.

In accordance with my invention, 1 have provided a soft valve detectorfor radio signals or the like which is fully as sensitive as the bestgas detectors formerly constructed, and as regular and reliable in itsoperation as the vacuum detector. The detectors embodying my inventioncontain certain gases immune to the clean-up effect, particularly thegases of the rare or noble gas group, such as argon, helium, neon, andeven nitrogen. They are steady and reproducible'in operation.

The accompanying drawing shows in Fig. 1 a radio receiving systemcontaining a detector illustrative of the class of devices embodying myinvention; Figs. 2, 3 and 4 are diagramsshowing electricalcharacteristics of my improved detector, and Fig. 5

illustrates a specific form of electron tube embodying myinvention.

Referring to Figs. 1 and 5 of the drawing the device here illustratedcomprises an electron emitting cathode 1, consisting preferably of atungsten filament, adapted to M heated to incandescen ce by a battery 2,or other suitable means, an anode 3, consisting of tungsten,'molybdenum, nickel, or other suitable conductive material and a controlelectrode or grid 4, which in the par ticular embodiment of my inventionillustrated in the drawing consists of a wire wound over supports 5, 6,and is located be tween the cathode and the anode. The anode isfrequently known as the plate and the current flowing between thecathode and anode as the plate current. It is the function of the grid'to .vary the electrostatic field between the cathode and the anode, andthereby control the electron current. In the device shown in Fig. 5, thesupporting and conducting wires 5, 6, 7, 8, 9, 10 and 11 are sealedintoa stem 12 of a sealed glass bulb or envelope 13, having a base 13provided with. current-conveying terminals, only two of which are shownat 14.

As the first step to the evacuation of the device the glass bulb 13 isevacuated while being heated to at least about 360 J, in fact, as high atemperature as the glass will withstand without collapsing in order todenude the same of gas. The anode 3 also is freed from disengageablegas, preferably by electronic bombardment in a vacuum, the pump beingconstantly operated. For this purpose the cathode is rendered incandescent and a voltage is applied to cause current flow between the cathodeand the anode to drive out gas in the now well-understood manner. Whenthe bulb and the electrodes have been made sufliciently gas-free, asubstantially immune to clean-up is admitted, for example, a rare gas,such as argon, helium, or neon. Nitrogen may also be used although notquite so effectively.

The envelope 13 is sealed when the gas pressure is in the range of about15 to '?5 microns, depending on the geometrical relation 01" theelectrodes. In the case of the construction illustrated in Fig. 5 apressure of about 20 to 60 microns is preferred.

The tube may be operated as detector in the usual, way in a radiosystem, for ex ample, as illustrated in Fig. 1. The grid 4 receivessignals from the antenna 18, for example. by being connected to thesecondary winding of a transformer winding 19 in series with a condenser20. The other terminal of the secondary winding is connected to thecathode 1. An ohmic resistance 23 may be connected in shunt to thecondenser 20, a switch 24 being provided to shortcircuit both thecondenser and resistance. An adjustable condenser 25 may be conneotedacross the transformer secondary. In circuit with the cathode 1 and theanode 3, some suitable receiving instrument. as for example, a telephonereceiver 21, is connected in series with: a suitable source of.

current, for example abattery 22.

Preferably the voltage of the battery 22 in the anode or plate circuitis adjusted somewhere above ionization voltage, but materially below thevoltage at which the ionization of gas in the detector becomes sointense that there is a tendency for a blue glow to form. Preferably,the operating plate voltage is about 18 to 23 volts. Under theseconditions the detector exhibits amarkedly superior sensitivity to thevacuum detector of the pliotron type. In practice, the plate voltage andthe filament current are varied until a maximum response is ob- 'tainedin the receiver and the optimum settings thus obtained are maintainedduring operation over a considerable period of time. iv

Apparently this sensitivity is due to certain critical conditions ofthe'tube which may be explained at least in part by reference to thegrid and plate characteristics, as illustrated in a conventional mannerin Figs. 2, 3 and 4. In Fig. 2 I have shown plotted for illustrativepurposes a representative set of readings of plate currents plottedasordinates and plate voltages as abscissae. The currents obtained withdifferent impressed volatges in a device evacuated so highly that theionization of residual gas is negligible is represented by the curve 26,which over a short region, say, above about 10 to 15 volts,substantially obeys the 3/2 power law of pure electron conduction. Inother words, the currents obtained with different impressed voltagesvary directly with the 3/2 power of the voltage. In a tube constructedin accordrising voltages varies with a higher and ance with my inventionand containingv ionizable gas, the increase of current with constantlyincreasing power causing the characteristic to be more steeply curved,as illustrated by the curve 27.

Related intimately to this plate circuit characteristic is thegrid-voltage, plate-current characteristic as illustrated in Fig. 3.When in a given tube different steady voltages are applied to the platecircuit, and

the grid voltage is varied below and above zero, a series ofcorresponding plate currents are obtainable. In Fig. 3 the curve 28represents the relation of grid voltage of a vacuum tube above and belowzero to current in the plate circuit with a steadily applied platevoltage of 40/ volts. In a tube embodying my invention, the change ofcurrent obtained by varying the grid voltage with a steadily appliedplate voltage of 20 volts is illustrated by the curve 29. This curve issteeper even at the lower plate voltage and not as straight as the curve28.

The slope of the curve thus obtained is usually designated as rho. Inother, words. the value of rho represents the relation of the change ofcurrent in the plate circuit. in micro-amperes to the change of voltagein the grid circuit in volts. This value is also known as theconductance of the tube and is usually expressed in microbnis.

Fig. 4 illustrates the conductance of the tube at different platevoltages. The conductances are plotted in microhms as ordinates, and theplate voltages are plotted asabscissae. It will be observed thatthecurve 30 expressing the conductance of a high vacuum or hard tube has agentle uniform slope. On the other hand, the curve 31 expressing; theconductance of a soft'tube embodying my invention, follows very closelyto the curve of the vacuum tube up to a value of about 16 volts, andthen very sharply bends upward and becomes almost vertical. In otherwords, at and above the ionization voltage of the gas filling in thetube, the conductance of the tube varies very rapidly with differentplate voltages. Inv fact, results indicate that at some voltages in arange above and in the neighborhood of the ionization the conductancevaries even more abruptly than indicated b the conventional; curve shownin the di agram. When a tube embodying my invention is operated as adetector with a plate potential. above ionization voltage. say. at 18 to23 volts. which is well below the voltage at which the ionizationbecomes so intense as to produce a glow. the rate of change ofconductances is high andv there fore the rate of change of current in areceiver circuit is correspondingly great. As a result the device isvery sensitive to feeble variations of voltage in the grid circuit,such, as for example, produced by weak radio signals.-

In the soft tubes formerly produced this condition of sensitivity wasextremely variable and erratic due to the continual variation of the gascontent of the tube. This variation was apparently due to the liberationof gas from the parts of the tube, particularly the bulb, and thesimultaneous clean-up of gas was due to chemical and physical actionwithin the tube. In a detector tube embodying my invention these sourcesof variation are removed, the bulb and working parts of the tube havingbeen freed from disengageable gas and the gas filling beingsubstantially immune to cleanup eflects. Whatever may be the correctexplanation, the characteristics of my device are steady andreproducible, as contrasted with the unsteady and non-reproduciblecharacteristic of soft tubes heretofore known. The device is soexceedingly sensit-ive in its operation that it is probable that theoperation of the same involves phenomena not at present apprehended.

While I have described the operation of my improved detector asinvolving the ionization of the low pressure gaseous filling therein, Ido not wish to be limited by this theory of operation as the benefits ofmy invention may be obtained independently of any particular theoryofoperation.

What I claim as new and desire to secure by Letters Patent ofthe UnitedStates, is

1. An electron discharge device comprising a sealed container, a cathodeadapted to operate at incandescence, an anode, a chargereceiving memberor grid for controlling a current in said device, the container andparts of said device being substantially deprived of disengageable gas,and a filling of gas substantially immune to clean-up effects at apressure of about 15 to 75 microns in said container.

2. An electron discharge device comprising a sealed container, a cathodeadapted to emitelectrons, an anode, means for varying the electrostaticfield about said electrodes,-the walls of said container and theelectrodes being substantially deprived of disengageable gas, and a gasfilling substantially immune to clean-up effects and non-condensible atordinary temperatures sufiicient in amount to produce at a given voltagebetween said cathode and anode by a progressive change of theelectrostatic field in the positive direction, a corresponding regularincrease of current between said electrodes which is greater than theincrease under the same conditions in a similar device in which theresidual gas is negligible, said gas content being insufiicient toproduce blue glow under operating conditions.

3. A radio detector comprising a sealed container, a filamentary cathodeadapted to be heated to incandescence, an anode, a grid locatedintermediate said electrodes and a quantity of rare gas at a pressure ofabout 15 to 7 5 microns of mercury, said container and electrodes beingdeprived of disengageable gas, said device being capable of operation atvoltages impressed on said electrodes above ionization voltage and belowa luminosity producing voltage.

4. A radio detector comprising the comgreater than the 3/2 power-of thevoltage, the pressure of said gas being insufiicient to enable anarc-like discharge to occur therein.

5. A radio detector comprising the combination of a cathode adapted toemit electrons by incandescence, an anode, a discharge controlling grid,an enclosing envelope, a filling of argon gas therein at a pressure ofabout 15 to 7 5 microns of mercury, a source of current having a voltageabove ionization voltage but insuficient to produce a luminous dischargein said gas in circuit with said cathode and anode, the quantity of saidgas filling being suficient to cause the current in said circuit to varywith variations ofvoltage over a working range at a rate materiallygreater than the 3/2 power of the voltage .but being insulficient topermit an arc-like discharge to occur therein atthe voltage of saidsource.

6. A radio detector comprising a sealed container, a cathode operable atincandescence, an anode or plate, a charge-controlling electrode or gridand a filling of gas at a pressure of about 20 to microns of mercury,said container and electrodes being deprived of gas, the conductance ofsaid detector increasing more rapidly with rise of plate voltage abovethe ionization voltage of said gas filling than would be the case insaid device were the residual gas at materially lower pressure.

7. A detector for radio signals comprising the combination of a sealedbulb, a cathode therein adapted to emit electrons, a plate or anode, thebulb, walls and contained members being substantially freefromdisengageable gas, a filling of attenuated gas which is substantiallyimmune to electrical clean-up efiects, a source of current connected incircuit with said cathode and anode having a voltage above and adjacentto the ionization voltage of said gas,-the pressure of gas in said bulbbeing so related to the voltage of said source that the variation ofconductance of said detector with variation of plate potential ismaterially greater than when gas Ionization is negligible.

8. A detector for radio signals com rising the combination of a sealedbul a cathode operable at incandescence, an anode anda grid therein, theparts of said device 139 being substantially free from disengageablegas, a rare or noble gas thereinat a pressure of about 15 to 75 micronsof mercury, and a source of potential of about 18 to 23 volts connectedbetween said cathode and anode.

9. An electrical discharge device comprising a container, an attenuatedgas therein which is substantially immune to cleanup effects, a cathodeoperable at incandescence, means for heating said cathode, an anode, acontrol electrode, said container and electrodesbeing deprived ofdisengageable gas, and a source of current at a voltage of about 18 to23 volts connected between said cathode and anode, the pressure of thegaseous filling being so chosen that the current between cathode andanode varies .more abruptly with variations of potential of the controlelectrode than whenthe residual gas pressure is so low that ionizationeffects are negli ible.

10. A radio etector apparatus comprisinga sealed container, afilamentary cathode of refractory material, an anode, a grid, saidcontainer and electrodes being deprived of gas, a filling of argon at'apressure of about 20 to 60 microns, a source of current at a voltage ofabout 18 to 23 volts connects ed between said cathode and anode andmefins for impressing radio signals'on said gri In witness whereof, Ihave hereunto set my hand this27th day of October 1920.

WILLIAM C. WHITE.

